Control system for aircraft turbosuperchargers



Nov. 16, 1948. F. E. CREVER CONTROL SYSTEM FOR AIRCRAFTTURBOSUPERCHARGERS Filed Oct. 14, 1942 r W 9. r m w w E it wk t m W .ITF.6

Patented Nov. 16, 1948 CONTROL SYSTEM FOR AIRCRAFT TURBOSUPERCHARGERSFrederick E. Crever, Scotla, N. Y., assignor to General ElectricCompany, a corporation oi New York Application October 14, 1942, SerialNo. 481,969

11 Claims.

My invention relates to a control system for aircraft turbosuperchargersand especially to control systems for turbosuperchargers wherein theturbosupercharger is operated by exhaust gases from an aircraft internalcombustion engine and the air compressed by the turbosupercharger isused to supercharge the engine. Specifically, my invention is animprovement on the control system disclosed and claimed in theapplication of David R. Shoults, Serial No. 452,294, filed July 25,1942, now matured into Patent No. 2,374,708 of May 1, 1945 and assignedto the same assignee as the present application.

An object of my invention is to provide a new and improved controlsystem for turbosuperchargers for aircraft.

Another object of my invention is to provide regulating means forturbosuperchargers which maintain a constant inlet manifold pressureover a predetermined range of operation with great stability.

Still another object of my invention is to provide new and improvedmeans for regulating a turbosupercharger in which constant inletmanifold pressure is maintained over. a predetermined range of operationthereof and thereafter substantially constant turbosupercharger speed ismaintained.

Further objects and advantages of my invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of my invention reference may be had to theaccompanying drawing in which the single figure thereof is adiagrammatic view of a turbosupercharger control system embodying myinvention.

Referring now to the drawing, It indicates an aircraft internalcombustion engine having'an intake manifold M and an exhaust manifoldl2. A carburetor I3 is schematically indicated as having its outletconnected to the intake manifold H by means of a conduit l4. Exhaustmanifold I2 is connected by a, conduit l5 to a nozzle box It of anexhaust gas-driven supercharger generally indicated at H. The turbinewheelv of the supercharger i1 is indicated at I8 and the compressor atl9. Connected with the nozzle box It is a waste conduit 20 in which islocated an adjustable waste gate valve 2| used in regulating theturbosupercharger. On the shaft of gate valve 2| is fixed an arm 22 foruse in positioning the valve.

Connected to the inlet of centrifugal compressor I9 is an intake conduit23 for conveying air from the slip-steam of the aircraft to thecompressor. To this end conduit 23 may be connected with a suitable ram,not shown, whichv faces into the slip-stream of the aircraft. Thedischarge side of compressor i9 is connected by a conduit 24 to theinlet of carburetor i3. Ii desired a suitable inter-cooler may beprovided in conduit 24 to maintain the temperature of the air enteringcarburetor l3 within a predetermined range for best airplaneperformance.

The arrangement so far described is a known one and is to be taken astypical of any suitable turborsupercharger installation. In operation,exhaust gases from the aircraft engine are supplied through conduit |5to the nozzle box It from which they are discharged through a'ring ofnozzles to the turbine wheel l8 of turbosupercharger H or, through wasteconduit directly to atmosphere. When waste gate valve 2| is wide opensubstantially all the exhaust gases discharge directly to atmosphere,little if any passing through the nozzles to the turbine wheel. Thisrepresents no load on the supercharger. As waste ate valve 2| isgradually closed pressure isbuilt up in nozzle box l6 effecting agradually increasing flow of exhaust gases through the nozzles to theturbine wheel to operate the supercharger. Maximum load on thesupercharger is reached when waste gate valve 2| is fully closed so thatall gases from the engine are discharged against the turbine wheel l8.Ordinarily, waste gate valve 2| is in an intermediate position, part ofthe exhaust gases bein discharged to atmosphere and the remainderpassing through the turbine wheel.

My invention has to do particularly with an improved means forregulating waste gate valve 2|.

The position of waste gate valve 2| may be varied by any suitable motivemeans such, for example, as a hydraulic piston or the like. However, dueto the very low temperatures encountered by high flying aircraft theoilused' to operate a piston or similar motive means is likely tocongeal and unsatisfactory operation result. Preferably therefore, Icontrol the position of waste gate valve 2| through operation of motivemeans comprising an electric motor 25 of the split series field typehaving field windings 25a and 2512. Upon proper energization of motor 25it will, as desired, rotate in either direction. The

- shaft 26 of motor 25 is connected through suitable gearing 21, aclutch 28 and a linkage mechanism generally indicated at 29 to arm 22controlling the position of waste gate valve 2|. Associated with thelinkage mechanism indicated at 29 are centering springs 30 whichmaintain waste gate valve 2| in an intermediate position whenever theclutch 28 is disengaged. The centering springs 30 are associated with alever 3| attached to the linkage mechanism 29. Lever 3| is provided withan extension 32 for engaging in either extreme position thereof withnormally closed it switches 33 and 34 connected in the energizationcircuits of motor 25, thereby to prevent over-travel of waste gate valve2|.

The clutch 24 is normally biased by spring means 35 to the disengagedposition. However, a solenoid 34. is provided causing engagement ofclutch 24, which solenoid is energized continuously except upon failureof electrical power supply, in which case the centering springs movewaste gate valve 2 l' to an intermediate position.

In order accurately to control the operation of motor 25 with regard towaste .gate valve 2|, a

suitable brake 31 is provided which is normally biased by spring means38 to the engaged position and is electrically released by means of asolenoid 33 which is energized simultaneously with energization of motor24.

In order to operate motor 25, solenoid operated brake 81 and solenoidcontrolled clutch 23 I provide a source of control potential generallyindicated at 4| which is connected through a master control switch 4| tosolenoid 38 and through master control switch 4| and automaticallyoperable double-throw switch 42, specifically illustrated as a vacuumswitch, to motor 25, and solenoid 3!. Vacuum switch 42 is provided witha movable switching member 43 for completing the circuit between oneterminal of source and one or the other bf a pair of stationary contacts44 or 45. Contact 44 is connected through limit switch 33, series field2Ia and motor 25 to parallel connected solenoid 33 of the brakeassociated with motor 2!. Similarly, terminal 45 of vacuum switch 42 isconnected through limit switch 34 and series field 25b and motor 25 toparallel connected solenoid 3! and the brake associated with motor 25..When wastegate valve 2 I .is reguJated automatically by .the regulatorto. be described hereinafter, master control switch 4| will be closed.If switching member 43 is now moved to engage contacts 44, series fleld25a will be energized to cause rotation of motor 25 in such a direction,as to move gate valve 2| in a closing direction. Conversely, ifswitching member 43 engages contact 45 series field 25b is energized tocause rotation of motor 25 in a direction to open waste gate valve 21.When switching member 43 is in an intermediate position engaging neithercontacts 44 nor 4!, motor 25 is deenergized and brake 31 preventsfurther rotation thereof.

The operation of motor 25 and consequently the position of gate valve 2|may be controlled,.

as will be obvious from the following description, in response to anycontrol pressure appiu'tenant to an operating condition of thesupercharger i1. As was mentioned above, however, over the normaloperating range of the supercharger-until a predetermined critical speedis reached, it is desirable to regulate the operation thereof tomaintain constant the inlet manifold pressure of the aircraft engineassociated with the supercharger. To this end I provide apressure-responsive mechanism for operating switching member 43 ofvacuum switch 42 in accordance with the particular control pressure orcontrol condition appurtenant to the operation of turbosupercharger I!which it is desired to maintain.

As shown in the drawing, I provide a pressureresponsive device whichaids in regulating the discharge pressure of the .turbosuperchargercompressor to a value which is adjustable by the pilot until thecritical speed of the turbosupercharger is reached, the speed beingroughly proportional to the pressure ratio across the compressorthereof, and thereafter'to regulate the speed based vol on this pressureratio to limit the maximum speed of the turbosupercharger. regulatorcomprises a movable control or regulating member 4. pivotally mounted at41. Suitable controlling forces are applied to movable regulating member4' as will be described hereinafter which controlling forces aretransmitted to switching member 43 of vacuum switch 42 by means of alink 43 inter-connecting one end of member 48 with switching member 43.In order to amplify the movement produced by the control forces appliedto regulating member 48 the control forcesare applied to member 46through fairly short lever arms as contrasted with the long lever armfor transmitting these forces to switching member 43. Preferably movablecontrol member 48 and vacuum switch 42 are inouriged within afluid-tight enclosure or hous- Mounted within fluid-tight housing 49 isa regulator member generally indicated at B0 which comprises an outerbellows member BI and an inner bellows member I2 concentrically arrangedwith respect to one another. One adjacent end of each of bellows membersBI and 52 is connected to a stationary member 63 while the other endsare connected directly to movable regulating member 48 as indicated at54 through a relatively short lever arm with reference to member 46. Theinterior of bellows II is evacuated while the interior of bellows 52 isconnected directly to the control pressure which it is desired toregulate through conduit 6| which, as indicated in the drawing, isconnected to the discharge of compressor is so as to regulate thecompressor discharge pressure or, in other words, the intake manifoldpresure.

Also connected to movable regulating member 46 through the same leverarm as regulating member 50 is a second regulating member generallyindicated at 58 which comprises a single bellows 51 having the samecross-sectional area as bellows 5|. One end of bellows 51 is connectedto a stationary member 88 while the other end thereof isconnected'through a disconnecting link i9 comprising a pair of hookedfingers, to point 54 on movable regulating member 48. Bellows 51 whichis evacuated contains a compression spring 80. In order to make itpossible to adjust the pressure to be regulatedat the will of the pilotas long as the predetermined critical speed of the supercharger is notexceeded, I provide a manual, adjustment lever 6| which is connected bylever 62, tension spring 63 and lever 64 to the free movable and ofbelows 51. If the pilot moves manual lever 61 to change the tension onspring 63 the pressure of the quantity which it is desired to regulateby the automatic regulator covered by my invention may be varied oradjusted. A suitable stop BI is provided to limit the movement ofbellows l1 and permit the disconnecting link 69 to be describedhereinafter to function only when a certain predetermined operatingcharacteristic of the-turbosupercharger is attained.

In order to control movable regulating member 48 in response to theabsolute compressor discharge pressure or intake manifold pressureduring the range of operation below a predetermined maximum speed ofturbosupercharger I1, I connect housing 43 with the compressorintakeconduit 23 by means of a conduit 68 so that the interior of housing 48is maintained'at the compressor intake pressure. Since bellows 51 and5.1 have the same cross-sectional area the forces ex- I'his fluidpressure erted thereon by the compressor intake pressure are neutralizedinsofar as movable regulatin member 45 is concerned and since bellows isevacuated the only force acting on member 45 other thanthe-substantially constant force of springs 60 and 63 is thattransmitted by bellows 52 namely the absolute compressor dischargepressure or intake manifold pressure. This, of course, is only true aslong as disconnecting link 59 is in engagement as indicated in thedrawing. During such condition the following equation applies to thesystem:

in which Pi is the compressor inlet pressure, Po the compressor outletpressure, A51 is the area of bellows 51, A51 is the area of bellows 5|,A52 is the area of bellows 52 and K5 is the total spring force of thesprings 60 and 63. I

omitting the function of a bimetallic strip, described below, a force istransmitted through the hooks of the connecting link 59 which isrepresented by the lefthand part of the equation,

- namely, PlAST-KS. This force becomes zero when PiA5'1 is equal to Ks.When this takes place as will be readily seen from the above equation,the

pressure ratio g: is equal to 2:

In other words, the hooks of the connecting link 59 become disengagedonly at a predetermined ratio of the inlet and outlet pressures of thecom- .pressor. The bellows assembly 56 and the biasing spring 63 are sodesigned that when the aircraft is flying at a comparatively lowaltitude a quite appreciable upward force is exerted on thedisconnecting link 59. Since at low altitude the compressor inletpressure is comparatively high, this pressure communicated to theinterior of the re ulator casing 49 will cause the bellows assembly 59to tend to collapse, thus providing the downward reaction on the link 59needed to balance the above-mentioned upward force produced by,

the bellows assembly 56 and spring 63. Under such conditions, the.pressures to which the bellows assemblies 56 and 50 are subjectedcooperate to position the lever 46 in accordance with the value of thecompressor discharge pressure communicated to the interior of bellows52.

If new the aircraft should begin to climb, the

bellows combination 50, 56 will act to maintain constant the compressordischarge pressure. However, the decreasing pressure inside casing 49results in a decrease in the upward force exerted by bellows assembly'56, and spring 63 on the disconnecting link 59; while the increasingdifierential between the pressure inside of bellows 52 and that on theexterior of bellows 5| produces a corresponding decrease in the.downwardreaction force imposed on lever 46 by bellows assembly 50. As thealtitude increases, the above-described decrease in the forces exertedon the disconnecting link. 59 continues until a critical point isreached at which the hooks of the disconnecting link 59 just engagewithout any interchange of force.

If then the inlet pressure drops still further, the movable head ofbellows assembly 56 will continue its downward movement and the head ofbellows 59 its upward movement, thus producing disengagement of thehooked members comprising the disconnecting link 59. With the bellowsassembly 56 thus rendered ineffective by reason of disengagement of thehooks 59, the lever 46 will be positioned by the bellows assembly 50acting alone 6' (not taking into account the action of the bimetallicthermal element 61 described below).

If constant compressor inlet temperature and constant fluid conditionsof the supercharger obtain, the ratio of the compressor dischargepressure to the compressor inlet pressure is substantially proportionalto the speed of the compres-' sor. And even though the inlet temperatureand pressure vary, this pressure ratio gives a fairly accurate measureof the speed of the turbosupercharger. When the speed of theturbosupercharger reaches a predetermined maximum, it is desirable to nolonger try to maintain-constant the intake manifold pressure of theengine but rather to maintain constant the speed of the supercharger ator below a predetermined maximum value. By suitably proportioning theareas of bellows 5|, 52 and 51, a predetermined increase in the pressureratio between the compressor discharge pressure and the compressorintake pressure due to the fact that the aircraft has reached analtitude at which the compressor intake pressure has fallen apredetermined amount will permit compression spring 69 to move the freeend of bellows 51 downwardly so that lever 64 engages sto 65. Thereafterany increase in compressor discharge pressure will cause disconnectinlink 59 to effectively disconnect the movable ends of bellows 5| and 51so that thereafter only regulator 56 will be operably connected toregulating member 46. It should be understood, however, thatdisengagement of disconnecting link 59 is not limited to situations whenlever 64 engages stop 65 but may be determined by the design of thebellows, springs, and related parts, as described above. Since controlmember 50 includes bellow-s 5| subjected to the compressor intakepressure and bellows 52 subjected to the compressor discharge pressurewhich act in opposition to each other, a force proportional to the ratioof the compressor discharge pressure to the com .pressor inlet pressurewill be applied to member 46 or, in other words. a force substantiallyproportional to the speed of the turbosupercharger. By suitablyproportioning the areas of bellows 5| and 52 the control of movableregulating member 46 may be accomplished to maintain a desiredpredetermined pressure ratio, and consequently a predetermined maximumspeed.

Analysis and experience have shown that centrifugal compressor speed isnot a fixed function of pressure ratio, the relation varying somewhat asa function of inlet temperature. In order that disconnecting link 59 maybe op rated more exactly in response to the attainment of a pedetermined maximum speed of turbosupercharger disconnecting link 59 isby-passed by a bimetallic temperature compensator" illustrated ascompensating strip or spring 61. As was pointed out above,. the ratio ofthe compressor discharge pressure to the compressor inlet pressure wouldbe a true measure of compressor speed under constant flow and constantinlet temperature conditions. The pressure responsive bellows 51, 5|, 52and the springs Elland 63 and related parts are designed to give thedesired operation with some selected compressor inlet temperature. Ifthen,

, unless special compensating means are provided,

the inlet temperature should vary appreciably from this design value,the speed maintained by,

1 noted that because of the severe operating conditions encountered inaircraft turbo'superchargers, a variation of 10 per cent from thedesired speed might mean the difference between safe operation anddisaster. The, functio n of the bimetallic thermal element 81 is tointroduce a modifying or compensating force which will substantiallyeliminate the efiect of this variation in the'sneed versus pressureratio relation as compressor inlet temperature changes. It should benoted that the regulator housing 4! will be located in the aircraftin aposition where the entire casing and the elements contained therein willbe subject to ambient altitude temperature. Thus the thermal element 81will respond to changes in ambient altitude temperature, which issubstantially the same as compressor inlet temperature.

In designing the bimetallic thermal element 81, it is necessary to firstdetermine the variation of the relation between compressor pressureratio Y change of exhaust manifold pressure. Due to the will be obviousfrom-the drawing, produces a force and speed as the inlet-temperaturevaries. Having given this information, it is possible by analysis andcalculation, supported by tests. to design a bimetallic element whichwill produce the compensating force required to give a closely fixedrelation between speed and compressor pressure ratio regardless of inlettemperature. The design will be such that with the design temp rature"for which the bellows and springs were calculated to give the desiredeffect, the compensating force exerted by the bimetallic element on thedisconnecting link 59 is zero. With thistemperature; the hooks of thedisconnecting link will disengage at a predetermined pressureratiocorresponding to the maximum desired compressor speed. However asthe inlet temperature varies from the design temperature, thedisengagement of the hooks will take place at a pressure ratio whichvaries in the predetermined manner as a function of inlet temperature,so that the disengagement 01' the hooks always occurs at the preselectedcritical speed. Thus by the addition of the thermal compensating element61, the bellows arrangement. can be made to respond more exactly to theattainment; of a preselected maximum compressor speed.

To stabilize the operation of-the control mechanism I provide ananti-hunting device 88 omprising a pair of bellows 88 and 10, eachhaving one end thereof, namely the movable end connected in opposedrelationship to regulating member 48 at H through a relatively shortlever arm. thereby to magnify the movement thereof at the end of member48 which is connected to switching member 43 of vacuum switch 42. Theother end of bellows 89 is connected to a stationary member 12.Similarly the other end of bellows I is connected to a stationary member13.

The interiors of bellows 69 and I0 are connected through conduit 14 withconduit I so as to be responsive to the exhaust manifold pressure. Inorder that the anti-hunting device 68' may operate in response to therate of change of exhaust manifold pressure, I provide a restriction ororifice 15 between conduit I4 and the entrance .to bellows 10. Understeady exhaust manifold pressure conditlons the pressures in bellows B8and are equal and the'forceapplied by anti-hunting device 68 to member46 is zero. However, a change in exhaust manifold pressure will beimmediately effective in creating a force against the movable end ofbellows 69 which is connected to conduit II through a free passageway,whereas the change in force on the movable end of bellows Ill connectedthrough the restriction will be delayed, and consequently anti-huntingdevice ll on movable member 4! tending to maintain it in an intermediateposition.

Due to the fact that thebellows II, 2.11, I and II and Sp in s 6. and Iare connected to movable regulating member 4!, a fairly high force mustbe applied to member 46 to obtain movement and it might be desirable toprovide some means having a negative spring rate or constant forcounteracting this effect whereby greater sensitivity of the device maybe obtained. To this end I provide an armature II on movable regulatingmember 4 which is attracted by a suitable malnet 80 fixedly mounted inspaced relationshi thereto. 7 The operation of the turbosuperchargerreg.- ulator described above will be fairly obvious from the detaileddescription included above. Assume that the air craft is in the air andis flying at an altitude lowe thanthe critical altitude of thesupercharger, i. e., at an altitude below the maximum for which thesupercharger is capable of maintaining. without excess speed,apredetermined pressure on the discharge side oi the coinpressorfforexample, sea-level pressure. Also assume that at such altitude wastegate valve II is in a partially closed position and the supercharger isoperating at a speed such that the deg sired pressure obtains on thedischarge side 01' compressor is of the supercharger l1. Under theseconditions the compressor inlet pressure will be sumciently high and theratio of compressor discharge pressure to-compressor inlet is inengagement as shown in the drawing. In

this case movement of the free end of bellows 61 will cause movement ofmovable regulating member 48. Under these conditions, since the forcesapplied by bellows II and II to member 46 neutralize each other, member4. will-be op erated in direct response to the absolute compressordischarge pressure, or in other words, the intake manifold pressure. If,new, the prese sure on the discharge side of compressor II decreases,the end of lever '46 connected to bellows 5i and 52 will move downwardlyand such movement will be transmitted to switching member 43 ofvacuu'mswitch 42 to engage contact 44, whereupon motor 25, serieswinding 25a and electrical damping means 18 are energized, brake 31 isreleased, and waste gate valve II is rotat edin a closing direction .toincrease the speed of the supercharge and bring the compressor dischargepressure back to normah It is assumed, of .course, that master switch 4|is closed which would be the case when the regulator is operated. Whenswitch 4| is closed, the winding of solenoid 36 is continuouslyenergized to.

hold clutch 28 closed. On the other hand, if

produces a force dependent upon the rate of the pressure on thedischarge side of compressor It increases, then the end of member 4'con- .nected to bellows II and I: will be moved D- wardly and thismotion will be amplified by lever 46 to cause switching member ll ofvacuum switch 42 to engage contact ll, whereupon series field 25b, motor25, and solenoid 89 are energized as is also electrical damping means18. With this energization of motor-25, waste gate valve II is rotatedin an opening direction, whereby the speed of supercharger I1 isdecreased to brin the compressor discharge pressure back to normal. Anychange in the position of waste gate valve 2| will cause a very rapidchange in the exhaust manifold gas pressure so that anti-hunting device68 will apply force to member 48 in response to the rate of change ofexhaust gas manifold pressure and consequently will cause very stableoperation of movable regulating member it. The size of the restrictedopening I! and the area of bellows I and I are so chosen as to give theneeded counteracting or modifying effect to provide stable governing ofthe supercharger.

When the aircraft reaches the critical supercharger altitude. that is,the maximum altitude for which the supercharger is designed to maintainconstant compressor discharge pressure without exceeding a predeterminedmaximum speed, the ratio between the compressor discharge pressure andthe compressor inlet pressure will be such that the disconnecting link59 functions so that bellows 51 no longer exerts a force on movableregulating member 46. This occurs whenever the compressor inlet pressuremultiplied by the area of bellows 51- is less than the compressordischarge pressure multiplied by the area of bellows 52. This latterstatement is true except as modified by the action of the bimetallictemperature compensator 61 connected across the disconnecting link. Thisbimetallic temperature compensator modifies the pressure ratio at whichdisconnection of link 59 occurs, in order to correct for the effect ofinlet temperature on the relationship between turbosupercharger speedand the ratio of the compressor discharge and inlet pressures asdescribed above. When the link 59 is disconnected regulator 50 controlsmovable regulating member 46 in accordance with the pressure ratioreferred to above which is quite closely proportional to superchargerspeed by virtue of bimetallic temperature compensator 6'! assumingsubstantially constant fluid-flow conditions obtain. In other words,after the critical speed of the supercharger has been reached theregulating device of my invention will tend to maintain this speedconstant by adjusting the waste gate valve II in the same manner thatthe device tends to maintain the compressor discharge pressure constantover a predetermined range of operation.

With the invention described above it is possible to obtain closeautomatic and stable regulation of a turbosupercharger with an improvedapparatus that is very simple inconstruction and reliable in operation.

While I have shown and describe, a particular embodiment of my inventionit 11 be apparent to those skilled in the art that my invention is notlimited to the particular embodiment shown but that changes andmodifications may be made without departing from the spirit and scope ofmy invention and I aim in the appended claims to cover all such changesand modifications.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a turbine driven compressor actuated by exhaustgases, valve means for regulating the flow of exhaust gases to theturbine,

means responsive to the pressure of the air discharged from thecompressor for positioning said valve means to maintain the pressure ofthe air from said compressor at a constant value over a predeterminedrange of operation, and means responsive to the rate of change ofpressure of said exhaust gases in the turbine for modifying theeffective action of said last mentioned means to prevent hunting.

2. In combination, a turbine driven compressor actuated by exhaustgases, valve-means for regulating the now of exhaust gases .to theturbine,

. lating the flow of exhaust gases to the turbine,

means responsive to the discharge pressure of saidcompressor forautomatically positioning said regulating means during a predeterminedrange of operation of said compressor, a disconnecting link arranged tofunction upon operation of said compressor outside said predeterminedrange of operation to cause control of the position of said valve meansin response to the ratio of the discharge to the inlet pressure of saidcompressor, and means for modifying the effective action of said meansresponsive to the discharge pressure of said compressor in response tothe rate of change of pressure of the exhaust gases so as to preventhunting.

v 4. In combination, a turbine driven compressor actuated by exhaustgases, valve means for regu lating the flow of exhaust gases to theturbine,

an electric motor for positioning said valve means, a source of powerfor said electric motor, means responsive to a pressure which is ameasure of an operating condition of said turbine driven compressor tobe controlled'for automatically controlling said electric motor andconsequently positioning said valve means over a predetermined range ofoperation of said compressor, and means responsive to failure of sourceof power for causing said valve means to assume an intermediateposition.

5. The combination with a turbosupercharger comprising a gas driventurbine, a compressor driven from the turbine, an electric motor and apower supply therefor, and valve means for regulating the supply of gasto the turbosupercharger, of a control mechanism for said valve meanscomprising a movable regulating member for control- 1 ling theenergization of said electric motor connected to position said valvemeans, means for subjecting said regulating member to a force responsiveto the discharge pressure of said compressor, means for subjecting saidregulating member throughout a predetermined range of operation of saidturbosupercharger to equal and opposite forces responsive to the inletpressure of said compressor, means for rendering one of said lastmentioned forces ineffective with respect to said regulating member whena predetermined I ratio of compressor discharge to compressor inletpressure obtains and means for positioning said valve means in anintermediate position upon failure of said power supply for saidelectric motor.

6. In a regulator the combination of a control lever, a first evacuatedbellows assembly subjected externally to a first variable pressure andconnected to the control lever by a disconnecting link arranged so thatsaid first bellows can exert a force in one direction only on the lever,a second evacuated bellows subjected externally to the first pressureand connected to the control lever, and

a third bellows within the second evacuated bel- 1 lever, a firstevacuated bellows assembly subjected externally to a first variablepressure and connected to the control lever by a disconnecting linkarranged so that said first bellows can exert a force in one directiononly on the lever, a second evacuated bellows subjected externally tothe first pressure and connected to the control lever, a third bellowswithin the second evacuated bellows subjected internally to a secondvariable P essure and connected to the control lever, the bellowsassemblies and the disconnecting link being so constructed and arrangedthat when the ratio of the second to the first pressure is below acritical value all three bellows cooperate to position the lever inaccordance with the value of the second pressure while when said ratiois above the critical value the disconnecting link renders the firstbellows ineffective, and a thermal device responsive to a temperaturecondition connected to the lever and the first bellows .in parallel withthe disconnecting link and arranged to alter as a function of saidtemperature condition the value of pressure ratio at which the firstbellows becomes ineffective.

8. In combination with a centrifugal compressor driven by a gas turbinewith means for controlling the pressure of motive fiuid supplied to theturbine, a regulator for said control means including a, control lever,a first device responsive to compressor pressure ratio connected to thelever, a second device including an evacuated bellows subjected on itsexterior surface to compressor inlet pressure and spring means arrangedto act on the lever through a connection capable of transmitting forceto the lever in one direction only, the first and second devices beingarranged a,4c4,oss

to cooperatively position the lever in accordance with the value ofcompressor discharge pressure for all values of compressor pressureratio up to a predetermined maximum value and the oneway connectionbeing arranged to render the second device inefiective when the pressureratio reaches the predetermined maximum so that the lever is positionedby the first device to maintain the pressure ratio constant at saidmaximum value, and anti-hunting means responsive to the rate of changein pressure of the turbine motive fiuid connected to the lever tostabilize the action of the first and second devices.

9. In combination with a motor driven centrifugal compressor havingmeans for controlling the compressor speed, a regulator for said controlmeans including a control lever, a first device responsive to compressorpressure ratio connected to the lever, a second device including anevacuated bellowssubjected on its exterior surface to compressor inletpressure and spring means arranged to act on the lever through aconnection capable of transmitting force to the lever in one directiononly, the first and second devices being arranged to cooperativelyposition the lever in,

accordance with the value of compressor discharge pressure for'allvalues of compressor pressure ratio up to a predetermined maximum valueand the one-way connection being arranged to render the second deviceineifective when the pressure ratio reaches the predetermined maximum sothat the lever is positioned by the first device to maintain thepressure ratio constant at said maximum value.

10. In combination with a motor driven centrifugal compressor havingmeans for controlling the compressor speed, a regulator for said controlmeans including a control lever, a first device responsive to compressorpressure ratio connected to the lever, a second device including anevacuated bellows subjected on its exterior surface to compressor inletpressure and spring means arranged to act on the lever through aconnection capable of transmitting force to the lever in one directiononly, and a thermal device connected to the second device and to thelever in parallel pressor pressure ratio up to a predetermined maximumvalue, and the one-way connection and the thermal device being arrangedto render the second device inoperative when the pressure ratio reachesa maximum value corresponding to a preselected maximum speed of thecompressor.

11. Apparatus for controlling the pressure of the air supplied totheintake manifold of an internal combustion engine provided with aturbine-driven compressor for, supplying air to said intake manifold andpowered by exhaust gases from said engine, comprising in combination,means for controlling the pressure of said exhaust gases to control thespeed of said turbine and compressor, motor means for driving saidpressure controlling means, a device responsive to the pressure of theair supplied by said compressor, means including said device forcontrolling said motor means to maintain said intake manifold pressuresubstantially constant, a. device responsive to the rate of change ofthe pressure of said exhaust gases, means including said last-mentioneddevice for additionally controlling said motor means to limit theacceleration of said turbine.

FREDERICK E. CREVER.

\ REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Great Britain Jan. 28, 1938

